/**
    *    Copyright 2009-2019 the original author or authors.
    *
    *    Licensed under the Apache License, Version 2.0 (the "License");
    *    you may not use this file except in compliance with the License.
    *    You may obtain a copy of the License at
    *
    *       http://www.apache.org/licenses/LICENSE-2.0
    *
   *    Unless required by applicable law or agreed to in writing, software
   *    distributed under the License is distributed on an "AS IS" BASIS,
   *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *    See the License for the specific language governing permissions and
   *    limitations under the License.
   */
  package org.apache.ibatis.executor.resultset;
  
  import java.lang.reflect.Constructor;
  import java.sql.CallableStatement;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import java.sql.Statement;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Locale;
  import java.util.Map;
  import java.util.Set;
  
  import org.apache.ibatis.annotations.AutomapConstructor;
  import org.apache.ibatis.binding.MapperMethod.ParamMap;
  import org.apache.ibatis.cache.CacheKey;
  import org.apache.ibatis.cursor.Cursor;
  import org.apache.ibatis.cursor.defaults.DefaultCursor;
  import org.apache.ibatis.executor.ErrorContext;
  import org.apache.ibatis.executor.Executor;
  import org.apache.ibatis.executor.ExecutorException;
  import org.apache.ibatis.executor.loader.ResultLoader;
  import org.apache.ibatis.executor.loader.ResultLoaderMap;
  import org.apache.ibatis.executor.parameter.ParameterHandler;
  import org.apache.ibatis.executor.result.DefaultResultContext;
  import org.apache.ibatis.executor.result.DefaultResultHandler;
  import org.apache.ibatis.executor.result.ResultMapException;
  import org.apache.ibatis.mapping.BoundSql;
  import org.apache.ibatis.mapping.Discriminator;
  import org.apache.ibatis.mapping.MappedStatement;
  import org.apache.ibatis.mapping.ParameterMapping;
  import org.apache.ibatis.mapping.ParameterMode;
  import org.apache.ibatis.mapping.ResultMap;
  import org.apache.ibatis.mapping.ResultMapping;
  import org.apache.ibatis.reflection.MetaClass;
  import org.apache.ibatis.reflection.MetaObject;
  import org.apache.ibatis.reflection.ReflectorFactory;
  import org.apache.ibatis.reflection.factory.ObjectFactory;
  import org.apache.ibatis.session.AutoMappingBehavior;
  import org.apache.ibatis.session.Configuration;
  import org.apache.ibatis.session.ResultContext;
  import org.apache.ibatis.session.ResultHandler;
  import org.apache.ibatis.session.RowBounds;
  import org.apache.ibatis.type.JdbcType;
  import org.apache.ibatis.type.TypeHandler;
  import org.apache.ibatis.type.TypeHandlerRegistry;
  
  /**
   * @author Clinton Begin
   * @author Eduardo Macarron
   * @author Iwao AVE!
   * @author Kazuki Shimizu
   */
  public class DefaultResultSetHandler implements ResultSetHandler {
  
    private static final Object DEFERRED = new Object();
  
    private final Executor executor;
    private final Configuration configuration;
    private final MappedStatement mappedStatement;
    private final RowBounds rowBounds;
    private final ParameterHandler parameterHandler;
    private final ResultHandler<?> resultHandler;
    private final BoundSql boundSql;
    private final TypeHandlerRegistry typeHandlerRegistry;
    private final ObjectFactory objectFactory;
    private final ReflectorFactory reflectorFactory;
  
    // nested resultmaps
    private final Map<CacheKey, Object> nestedResultObjects = new HashMap<>();
    private final Map<String, Object> ancestorObjects = new HashMap<>();
    private Object previousRowValue;
  
    // multiple resultsets
    private final Map<String, ResultMapping> nextResultMaps = new HashMap<>();
    private final Map<CacheKey, List<PendingRelation>> pendingRelations = new HashMap<>();
  
    // Cached Automappings
    private final Map<String, List<UnMappedColumnAutoMapping>> autoMappingsCache = new HashMap<>();
  
    // temporary marking flag that indicate using constructor mapping (use field to reduce memory usage)
    private boolean useConstructorMappings;
 
   private static class PendingRelation {
     public MetaObject metaObject;
     public ResultMapping propertyMapping;
   }
 
   private static class UnMappedColumnAutoMapping {
     private final String column;
     private final String property;
     private final TypeHandler<?> typeHandler;
     private final boolean primitive;
 
     public UnMappedColumnAutoMapping(String column, String property, TypeHandler<?> typeHandler, boolean primitive) {
       this.column = column;
       this.property = property;
       this.typeHandler = typeHandler;
       this.primitive = primitive;
     }
   }
 
   public DefaultResultSetHandler(Executor executor, MappedStatement mappedStatement, ParameterHandler parameterHandler, ResultHandler<?> resultHandler, BoundSql boundSql,
                                  RowBounds rowBounds) {
     this.executor = executor;
     this.configuration = mappedStatement.getConfiguration();
     this.mappedStatement = mappedStatement;
     this.rowBounds = rowBounds;
     this.parameterHandler = parameterHandler;
     this.boundSql = boundSql;
     this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
     this.objectFactory = configuration.getObjectFactory();
     this.reflectorFactory = configuration.getReflectorFactory();
     this.resultHandler = resultHandler;
   }
 
   //
   // HANDLE OUTPUT PARAMETER
   //
 
   @Override
   public void handleOutputParameters(CallableStatement cs) throws SQLException {
     final Object parameterObject = parameterHandler.getParameterObject();
     final MetaObject metaParam = configuration.newMetaObject(parameterObject);
     final List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
     for (int i = 0; i < parameterMappings.size(); i++) {
       final ParameterMapping parameterMapping = parameterMappings.get(i);
       if (parameterMapping.getMode() == ParameterMode.OUT || parameterMapping.getMode() == ParameterMode.INOUT) {
         if (ResultSet.class.equals(parameterMapping.getJavaType())) {
           handleRefCursorOutputParameter((ResultSet) cs.getObject(i + 1), parameterMapping, metaParam);
         } else {
           final TypeHandler<?> typeHandler = parameterMapping.getTypeHandler();
           metaParam.setValue(parameterMapping.getProperty(), typeHandler.getResult(cs, i + 1));
         }
       }
     }
   }
 
   private void handleRefCursorOutputParameter(ResultSet rs, ParameterMapping parameterMapping, MetaObject metaParam) throws SQLException {
     if (rs == null) {
       return;
     }
     try {
       final String resultMapId = parameterMapping.getResultMapId();
       final ResultMap resultMap = configuration.getResultMap(resultMapId);
       final ResultSetWrappertset/ResultSetWrapper.html#ResultSetWrapper">ResultSetWrapper rsw = new ResultSetWrapper(rs, configuration);
       if (this.resultHandler == null) {
         final DefaultResultHandlertHandler.html#DefaultResultHandler">DefaultResultHandler resultHandler = new DefaultResultHandler(objectFactory);
         handleRowValues(rsw, resultMap, resultHandler, new RowBounds(), null);
         metaParam.setValue(parameterMapping.getProperty(), resultHandler.getResultList());
       } else {
         handleRowValues(rsw, resultMap, resultHandler, new RowBounds(), null);
       }
     } finally {
       // issue #228 (close resultsets)
       closeResultSet(rs);
     }
   }
 
   //
   // HANDLE RESULT SETS
   //
   @Override
   public List<Object> handleResultSets(Statement stmt) throws SQLException {
     ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
 
     final List<Object> multipleResults = new ArrayList<>();
 
     int resultSetCount = 0;
     ResultSetWrapper rsw = getFirstResultSet(stmt);
 
     List<ResultMap> resultMaps = mappedStatement.getResultMaps();
     int resultMapCount = resultMaps.size();
     validateResultMapsCount(rsw, resultMapCount);
     while (rsw != null && resultMapCount > resultSetCount) {
       ResultMap resultMap = resultMaps.get(resultSetCount);
       handleResultSet(rsw, resultMap, multipleResults, null);
       rsw = getNextResultSet(stmt);
       cleanUpAfterHandlingResultSet();
       resultSetCount++;
     }
 
     String[] resultSets = mappedStatement.getResultSets();
     if (resultSets != null) {
       while (rsw != null && resultSetCount < resultSets.length) {
         ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
         if (parentMapping != null) {
           String nestedResultMapId = parentMapping.getNestedResultMapId();
           ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
           handleResultSet(rsw, resultMap, null, parentMapping);
         }
         rsw = getNextResultSet(stmt);
         cleanUpAfterHandlingResultSet();
         resultSetCount++;
       }
     }
 
     return collapseSingleResultList(multipleResults);
   }
 
   @Override
   public <E> Cursor<E> handleCursorResultSets(Statement stmt) throws SQLException {
     ErrorContext.instance().activity("handling cursor results").object(mappedStatement.getId());
 
     ResultSetWrapper rsw = getFirstResultSet(stmt);
 
     List<ResultMap> resultMaps = mappedStatement.getResultMaps();
 
     int resultMapCount = resultMaps.size();
     validateResultMapsCount(rsw, resultMapCount);
     if (resultMapCount != 1) {
       throw new ExecutorException("Cursor results cannot be mapped to multiple resultMaps");
     }
 
     ResultMap resultMap = resultMaps.get(0);
     return new DefaultCursor<>(this, resultMap, rsw, rowBounds);
   }
 
   private ResultSetWrapper getFirstResultSet(Statement stmt) throws SQLException {
     ResultSet rs = stmt.getResultSet();
     while (rs == null) {
       // move forward to get the first resultset in case the driver
       // doesn't return the resultset as the first result (HSQLDB 2.1)
       if (stmt.getMoreResults()) {
         rs = stmt.getResultSet();
       } else {
         if (stmt.getUpdateCount() == -1) {
           // no more results. Must be no resultset
           break;
         }
       }
     }
     return rs != null ? new ResultSetWrapper(rs, configuration) : null;
   }
 
   private ResultSetWrapper getNextResultSet(Statement stmt) {
     // Making this method tolerant of bad JDBC drivers
     try {
       if (stmt.getConnection().getMetaData().supportsMultipleResultSets()) {
         // Crazy Standard JDBC way of determining if there are more results
         if (!(!stmt.getMoreResults() && stmt.getUpdateCount() == -1)) {
           ResultSet rs = stmt.getResultSet();
           if (rs == null) {
             return getNextResultSet(stmt);
           } else {
             return new ResultSetWrapper(rs, configuration);
           }
         }
       }
     } catch (Exception e) {
       // Intentionally ignored.
     }
     return null;
   }
 
   private void closeResultSet(ResultSet rs) {
     try {
       if (rs != null) {
         rs.close();
       }
     } catch (SQLException e) {
       // ignore
     }
   }
 
   private void cleanUpAfterHandlingResultSet() {
     nestedResultObjects.clear();
   }
 
   private void validateResultMapsCount(ResultSetWrapper rsw, int resultMapCount) {
     if (rsw != null && resultMapCount < 1) {
       throw new ExecutorException("A query was run and no Result Maps were found for the Mapped Statement '" + mappedStatement.getId()
           + "'.  It's likely that neither a Result Type nor a Result Map was specified.");
     }
   }
 
   private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
     try {
       if (parentMapping != null) {
         handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
       } else {
         if (resultHandler == null) {
           DefaultResultHandlerr.html#DefaultResultHandler">DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
           handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
           multipleResults.add(defaultResultHandler.getResultList());
         } else {
           handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
         }
       }
     } finally {
       // issue #228 (close resultsets)
       closeResultSet(rsw.getResultSet());
     }
   }
 
   @SuppressWarnings("unchecked")
   private List<Object> collapseSingleResultList(List<Object> multipleResults) {
     return multipleResults.size() == 1 ? (List<Object>) multipleResults.get(0) : multipleResults;
   }
 
   //
   // HANDLE ROWS FOR SIMPLE RESULTMAP
   //
 
   public void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
     if (resultMap.hasNestedResultMaps()) {
       ensureNoRowBounds();
       checkResultHandler();
       handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
     } else {
       handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
     }
   }
 
   private void ensureNoRowBounds() {
     if (configuration.isSafeRowBoundsEnabled() && rowBounds != null && (rowBounds.getLimit() < RowBounds.NO_ROW_LIMIT || rowBounds.getOffset() > RowBounds.NO_ROW_OFFSET)) {
       throw new ExecutorException("Mapped Statements with nested result mappings cannot be safely constrained by RowBounds. "
           + "Use safeRowBoundsEnabled=false setting to bypass this check.");
     }
   }
 
   protected void checkResultHandler() {
     if (resultHandler != null && configuration.isSafeResultHandlerEnabled() && !mappedStatement.isResultOrdered()) {
       throw new ExecutorException("Mapped Statements with nested result mappings cannot be safely used with a custom ResultHandler. "
           + "Use safeResultHandlerEnabled=false setting to bypass this check "
           + "or ensure your statement returns ordered data and set resultOrdered=true on it.");
     }
   }
 
   private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
       throws SQLException {
     DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
     ResultSet resultSet = rsw.getResultSet();
     skipRows(resultSet, rowBounds);
     while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
       ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
       Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
       storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
     }
   }
 
   private void storeObject(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue, ResultMapping parentMapping, ResultSet rs) throws SQLException {
     if (parentMapping != null) {
       linkToParents(rs, parentMapping, rowValue);
     } else {
       callResultHandler(resultHandler, resultContext, rowValue);
     }
   }
 
   @SuppressWarnings("unchecked" /* because ResultHandler<?> is always ResultHandler<Object>*/)
   private void callResultHandler(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue) {
     resultContext.nextResultObject(rowValue);
     ((ResultHandler<Object>) resultHandler).handleResult(resultContext);
   }
 
   private boolean shouldProcessMoreRows(ResultContext<?> context, RowBounds rowBounds) {
     return !context.isStopped() && context.getResultCount() < rowBounds.getLimit();
   }
 
   private void skipRows(ResultSet rs, RowBounds rowBounds) throws SQLException {
     if (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
       if (rowBounds.getOffset() != RowBounds.NO_ROW_OFFSET) {
         rs.absolute(rowBounds.getOffset());
       }
     } else {
       for (int i = 0; i < rowBounds.getOffset(); i++) {
         if (!rs.next()) {
           break;
         }
       }
     }
   }
 
   //
   // GET VALUE FROM ROW FOR SIMPLE RESULT MAP
   //
 
   private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
     final ResultLoaderMapltLoaderMap.html#ResultLoaderMap">ResultLoaderMap lazyLoader = new ResultLoaderMap();
     Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
     if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
       final MetaObject metaObject = configuration.newMetaObject(rowValue);
       boolean foundValues = this.useConstructorMappings;
       if (shouldApplyAutomaticMappings(resultMap, false)) {
         foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
       }
       foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
       foundValues = lazyLoader.size() > 0 || foundValues;
       rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
     }
     return rowValue;
   }
 
   private boolean shouldApplyAutomaticMappings(ResultMap resultMap, boolean isNested) {
     if (resultMap.getAutoMapping() != null) {
       return resultMap.getAutoMapping();
     } else {
       if (isNested) {
         return AutoMappingBehavior.FULL == configuration.getAutoMappingBehavior();
       } else {
         return AutoMappingBehavior.NONE != configuration.getAutoMappingBehavior();
       }
     }
   }
 
   //
   // PROPERTY MAPPINGS
   //
 
   private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
       throws SQLException {
     final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
     boolean foundValues = false;
     final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
     for (ResultMapping propertyMapping : propertyMappings) {
       String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
       if (propertyMapping.getNestedResultMapId() != null) {
         // the user added a column attribute to a nested result map, ignore it
         column = null;
       }
       if (propertyMapping.isCompositeResult()
           || (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))
           || propertyMapping.getResultSet() != null) {
         Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
         // issue #541 make property optional
         final String property = propertyMapping.getProperty();
         if (property == null) {
           continue;
         } else if (value == DEFERRED) {
           foundValues = true;
           continue;
         }
         if (value != null) {
           foundValues = true;
         }
         if (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive())) {
           // gcode issue #377, call setter on nulls (value is not 'found')
           metaObject.setValue(property, value);
         }
       }
     }
     return foundValues;
   }
 
   private Object getPropertyMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
       throws SQLException {
     if (propertyMapping.getNestedQueryId() != null) {
       return getNestedQueryMappingValue(rs, metaResultObject, propertyMapping, lazyLoader, columnPrefix);
     } else if (propertyMapping.getResultSet() != null) {
       addPendingChildRelation(rs, metaResultObject, propertyMapping);   // TODO is that OK?
       return DEFERRED;
     } else {
       final TypeHandler<?> typeHandler = propertyMapping.getTypeHandler();
       final String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
       return typeHandler.getResult(rs, column);
     }
   }
 
   private List<UnMappedColumnAutoMapping> createAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String columnPrefix) throws SQLException {
     final String mapKey = resultMap.getId() + ":" + columnPrefix;
     List<UnMappedColumnAutoMapping> autoMapping = autoMappingsCache.get(mapKey);
     if (autoMapping == null) {
       autoMapping = new ArrayList<>();
       final List<String> unmappedColumnNames = rsw.getUnmappedColumnNames(resultMap, columnPrefix);
       for (String columnName : unmappedColumnNames) {
         String propertyName = columnName;
         if (columnPrefix != null && !columnPrefix.isEmpty()) {
           // When columnPrefix is specified,
           // ignore columns without the prefix.
           if (columnName.toUpperCase(Locale.ENGLISH).startsWith(columnPrefix)) {
             propertyName = columnName.substring(columnPrefix.length());
           } else {
             continue;
           }
         }
         final String property = metaObject.findProperty(propertyName, configuration.isMapUnderscoreToCamelCase());
         if (property != null && metaObject.hasSetter(property)) {
           if (resultMap.getMappedProperties().contains(property)) {
             continue;
           }
           final Class<?> propertyType = metaObject.getSetterType(property);
           if (typeHandlerRegistry.hasTypeHandler(propertyType, rsw.getJdbcType(columnName))) {
             final TypeHandler<?> typeHandler = rsw.getTypeHandler(propertyType, columnName);
             autoMapping.add(new UnMappedColumnAutoMapping(columnName, property, typeHandler, propertyType.isPrimitive()));
           } else {
             configuration.getAutoMappingUnknownColumnBehavior()
                 .doAction(mappedStatement, columnName, property, propertyType);
           }
         } else {
           configuration.getAutoMappingUnknownColumnBehavior()
               .doAction(mappedStatement, columnName, (property != null) ? property : propertyName, null);
         }
       }
       autoMappingsCache.put(mapKey, autoMapping);
     }
     return autoMapping;
   }
 
   private boolean applyAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String columnPrefix) throws SQLException {
     List<UnMappedColumnAutoMapping> autoMapping = createAutomaticMappings(rsw, resultMap, metaObject, columnPrefix);
     boolean foundValues = false;
     if (!autoMapping.isEmpty()) {
       for (UnMappedColumnAutoMapping mapping : autoMapping) {
         final Object value = mapping.typeHandler.getResult(rsw.getResultSet(), mapping.column);
         if (value != null) {
           foundValues = true;
         }
         if (value != null || (configuration.isCallSettersOnNulls() && !mapping.primitive)) {
           // gcode issue #377, call setter on nulls (value is not 'found')
           metaObject.setValue(mapping.property, value);
         }
       }
     }
     return foundValues;
   }
 
   // MULTIPLE RESULT SETS
 
   private void linkToParents(ResultSet rs, ResultMapping parentMapping, Object rowValue) throws SQLException {
     CacheKey parentKey = createKeyForMultipleResults(rs, parentMapping, parentMapping.getColumn(), parentMapping.getForeignColumn());
     List<PendingRelation> parents = pendingRelations.get(parentKey);
     if (parents != null) {
       for (PendingRelation parent : parents) {
         if (parent != null && rowValue != null) {
           linkObjects(parent.metaObject, parent.propertyMapping, rowValue);
         }
       }
     }
   }
 
   private void addPendingChildRelation(ResultSet rs, MetaObject metaResultObject, ResultMapping parentMapping) throws SQLException {
     CacheKey cacheKey = createKeyForMultipleResults(rs, parentMapping, parentMapping.getColumn(), parentMapping.getColumn());
     PendingRelation deferLoad = new PendingRelation();
     deferLoad.metaObject = metaResultObject;
     deferLoad.propertyMapping = parentMapping;
     List<PendingRelation> relations = pendingRelations.computeIfAbsent(cacheKey, k -> new ArrayList<>());
     // issue #255
     relations.add(deferLoad);
     ResultMapping previous = nextResultMaps.get(parentMapping.getResultSet());
     if (previous == null) {
       nextResultMaps.put(parentMapping.getResultSet(), parentMapping);
     } else {
       if (!previous.equals(parentMapping)) {
         throw new ExecutorException("Two different properties are mapped to the same resultSet");
       }
     }
   }
 
   private CacheKey createKeyForMultipleResults(ResultSet rs, ResultMapping resultMapping, String names, String columns) throws SQLException {
     CacheKeyKey.html#CacheKey">CacheKey cacheKey = new CacheKey();
     cacheKey.update(resultMapping);
     if (columns != null && names != null) {
       String[] columnsArray = columns.split(",");
       String[] namesArray = names.split(",");
       for (int i = 0; i < columnsArray.length; i++) {
         Object value = rs.getString(columnsArray[i]);
         if (value != null) {
           cacheKey.update(namesArray[i]);
           cacheKey.update(value);
         }
       }
     }
     return cacheKey;
   }
 
   //
   // INSTANTIATION & CONSTRUCTOR MAPPING
   //
 
   private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
     this.useConstructorMappings = false; // reset previous mapping result
     final List<Class<?>> constructorArgTypes = new ArrayList<>();
     final List<Object> constructorArgs = new ArrayList<>();
     Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
     if (resultObject != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
       final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
       for (ResultMapping propertyMapping : propertyMappings) {
         // issue gcode #109 && issue #149
         if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) {
           resultObject = configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
           break;
         }
       }
     }
     this.useConstructorMappings = resultObject != null && !constructorArgTypes.isEmpty(); // set current mapping result
     return resultObject;
   }
 
   private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix)
       throws SQLException {
     final Class<?> resultType = resultMap.getType();
     final MetaClass metaType = MetaClass.forClass(resultType, reflectorFactory);
     final List<ResultMapping> constructorMappings = resultMap.getConstructorResultMappings();
     if (hasTypeHandlerForResultObject(rsw, resultType)) {
       return createPrimitiveResultObject(rsw, resultMap, columnPrefix);
     } else if (!constructorMappings.isEmpty()) {
       return createParameterizedResultObject(rsw, resultType, constructorMappings, constructorArgTypes, constructorArgs, columnPrefix);
     } else if (resultType.isInterface() || metaType.hasDefaultConstructor()) {
       return objectFactory.create(resultType);
     } else if (shouldApplyAutomaticMappings(resultMap, false)) {
       return createByConstructorSignature(rsw, resultType, constructorArgTypes, constructorArgs);
     }
     throw new ExecutorException("Do not know how to create an instance of " + resultType);
   }
 
   Object createParameterizedResultObject(ResultSetWrapper rsw, Class<?> resultType, List<ResultMapping> constructorMappings,
                                          List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix) {
     boolean foundValues = false;
     for (ResultMapping constructorMapping : constructorMappings) {
       final Class<?> parameterType = constructorMapping.getJavaType();
       final String column = constructorMapping.getColumn();
       final Object value;
       try {
         if (constructorMapping.getNestedQueryId() != null) {
           value = getNestedQueryConstructorValue(rsw.getResultSet(), constructorMapping, columnPrefix);
         } else if (constructorMapping.getNestedResultMapId() != null) {
           final ResultMap resultMap = configuration.getResultMap(constructorMapping.getNestedResultMapId());
           value = getRowValue(rsw, resultMap, getColumnPrefix(columnPrefix, constructorMapping));
         } else {
           final TypeHandler<?> typeHandler = constructorMapping.getTypeHandler();
           value = typeHandler.getResult(rsw.getResultSet(), prependPrefix(column, columnPrefix));
         }
       } catch (ResultMapException | SQLException e) {
         throw new ExecutorException("Could not process result for mapping: " + constructorMapping, e);
       }
       constructorArgTypes.add(parameterType);
       constructorArgs.add(value);
       foundValues = value != null || foundValues;
     }
     return foundValues ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;
   }
 
   private Object createByConstructorSignature(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) throws SQLException {
     final Constructor<?>[] constructors = resultType.getDeclaredConstructors();
     final Constructor<?> defaultConstructor = findDefaultConstructor(constructors);
     if (defaultConstructor != null) {
       return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, defaultConstructor);
     } else {
       for (Constructor<?> constructor : constructors) {
         if (allowedConstructorUsingTypeHandlers(constructor, rsw.getJdbcTypes())) {
           return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, constructor);
         }
       }
     }
     throw new ExecutorException("No constructor found in " + resultType.getName() + " matching " + rsw.getClassNames());
   }
 
   private Object createUsingConstructor(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, Constructor<?> constructor) throws SQLException {
     boolean foundValues = false;
     for (int i = 0; i < constructor.getParameterTypes().length; i++) {
       Class<?> parameterType = constructor.getParameterTypes()[i];
       String columnName = rsw.getColumnNames().get(i);
       TypeHandler<?> typeHandler = rsw.getTypeHandler(parameterType, columnName);
       Object value = typeHandler.getResult(rsw.getResultSet(), columnName);
       constructorArgTypes.add(parameterType);
       constructorArgs.add(value);
       foundValues = value != null || foundValues;
     }
     return foundValues ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;
   }
 
   private Constructor<?> findDefaultConstructor(final Constructor<?>[] constructors) {
     if (constructors.length == 1) {
       return constructors[0];
     }
 
     for (final Constructor<?> constructor : constructors) {
       if (constructor.isAnnotationPresent(AutomapConstructor.class)) {
         return constructor;
       }
     }
     return null;
   }
 
   private boolean allowedConstructorUsingTypeHandlers(final Constructor<?> constructor, final List<JdbcType> jdbcTypes) {
     final Class<?>[] parameterTypes = constructor.getParameterTypes();
     if (parameterTypes.length != jdbcTypes.size()) {
       return false;
     }
     for (int i = 0; i < parameterTypes.length; i++) {
       if (!typeHandlerRegistry.hasTypeHandler(parameterTypes[i], jdbcTypes.get(i))) {
         return false;
       }
     }
     return true;
   }
 
   private Object createPrimitiveResultObject(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
     final Class<?> resultType = resultMap.getType();
     final String columnName;
     if (!resultMap.getResultMappings().isEmpty()) {
       final List<ResultMapping> resultMappingList = resultMap.getResultMappings();
       final ResultMapping mapping = resultMappingList.get(0);
       columnName = prependPrefix(mapping.getColumn(), columnPrefix);
     } else {
       columnName = rsw.getColumnNames().get(0);
     }
     final TypeHandler<?> typeHandler = rsw.getTypeHandler(resultType, columnName);
     return typeHandler.getResult(rsw.getResultSet(), columnName);
   }
 
   //
   // NESTED QUERY
   //
 
   private Object getNestedQueryConstructorValue(ResultSet rs, ResultMapping constructorMapping, String columnPrefix) throws SQLException {
     final String nestedQueryId = constructorMapping.getNestedQueryId();
     final MappedStatement nestedQuery = configuration.getMappedStatement(nestedQueryId);
     final Class<?> nestedQueryParameterType = nestedQuery.getParameterMap().getType();
     final Object nestedQueryParameterObject = prepareParameterForNestedQuery(rs, constructorMapping, nestedQueryParameterType, columnPrefix);
     Object value = null;
     if (nestedQueryParameterObject != null) {
       final BoundSql nestedBoundSql = nestedQuery.getBoundSql(nestedQueryParameterObject);
       final CacheKey key = executor.createCacheKey(nestedQuery, nestedQueryParameterObject, RowBounds.DEFAULT, nestedBoundSql);
       final Class<?> targetType = constructorMapping.getJavaType();
       final ResultLoaderultLoader.html#ResultLoader">ResultLoader resultLoader = new ResultLoader(configuration, executor, nestedQuery, nestedQueryParameterObject, targetType, key, nestedBoundSql);
       value = resultLoader.loadResult();
     }
     return value;
   }
 
   private Object getNestedQueryMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
       throws SQLException {
     final String nestedQueryId = propertyMapping.getNestedQueryId();
     final String property = propertyMapping.getProperty();
     final MappedStatement nestedQuery = configuration.getMappedStatement(nestedQueryId);
     final Class<?> nestedQueryParameterType = nestedQuery.getParameterMap().getType();
     final Object nestedQueryParameterObject = prepareParameterForNestedQuery(rs, propertyMapping, nestedQueryParameterType, columnPrefix);
     Object value = null;
     if (nestedQueryParameterObject != null) {
       final BoundSql nestedBoundSql = nestedQuery.getBoundSql(nestedQueryParameterObject);
       final CacheKey key = executor.createCacheKey(nestedQuery, nestedQueryParameterObject, RowBounds.DEFAULT, nestedBoundSql);
       final Class<?> targetType = propertyMapping.getJavaType();
       if (executor.isCached(nestedQuery, key)) {
         executor.deferLoad(nestedQuery, metaResultObject, property, key, targetType);
         value = DEFERRED;
       } else {
         final ResultLoaderultLoader.html#ResultLoader">ResultLoader resultLoader = new ResultLoader(configuration, executor, nestedQuery, nestedQueryParameterObject, targetType, key, nestedBoundSql);
         if (propertyMapping.isLazy()) {
           lazyLoader.addLoader(property, metaResultObject, resultLoader);
           value = DEFERRED;
         } else {
           value = resultLoader.loadResult();
         }
       }
     }
     return value;
   }
 
   private Object prepareParameterForNestedQuery(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
     if (resultMapping.isCompositeResult()) {
       return prepareCompositeKeyParameter(rs, resultMapping, parameterType, columnPrefix);
     } else {
       return prepareSimpleKeyParameter(rs, resultMapping, parameterType, columnPrefix);
     }
   }
 
   private Object prepareSimpleKeyParameter(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
     final TypeHandler<?> typeHandler;
     if (typeHandlerRegistry.hasTypeHandler(parameterType)) {
       typeHandler = typeHandlerRegistry.getTypeHandler(parameterType);
     } else {
       typeHandler = typeHandlerRegistry.getUnknownTypeHandler();
     }
     return typeHandler.getResult(rs, prependPrefix(resultMapping.getColumn(), columnPrefix));
   }
 
   private Object prepareCompositeKeyParameter(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
     final Object parameterObject = instantiateParameterObject(parameterType);
     final MetaObject metaObject = configuration.newMetaObject(parameterObject);
     boolean foundValues = false;
     for (ResultMapping innerResultMapping : resultMapping.getComposites()) {
       final Class<?> propType = metaObject.getSetterType(innerResultMapping.getProperty());
       final TypeHandler<?> typeHandler = typeHandlerRegistry.getTypeHandler(propType);
       final Object propValue = typeHandler.getResult(rs, prependPrefix(innerResultMapping.getColumn(), columnPrefix));
       // issue #353 & #560 do not execute nested query if key is null
       if (propValue != null) {
         metaObject.setValue(innerResultMapping.getProperty(), propValue);
         foundValues = true;
       }
     }
     return foundValues ? parameterObject : null;
   }
 
   private Object instantiateParameterObject(Class<?> parameterType) {
     if (parameterType == null) {
       return new HashMap<>();
     } else if (ParamMap.class.equals(parameterType)) {
       return new HashMap<>(); // issue #649
     } else {
       return objectFactory.create(parameterType);
     }
   }
 
   //
   // DISCRIMINATOR
   //
 
   public ResultMaping/ResultMap.html#ResultMap">ResultMap resolveDiscriminatedResultMap(ResultSet rs, ResultMap resultMap, String columnPrefix) throws SQLException {
     Set<String> pastDiscriminators = new HashSet<>();
     Discriminator discriminator = resultMap.getDiscriminator();
     while (discriminator != null) {
       final Object value = getDiscriminatorValue(rs, discriminator, columnPrefix);
       final String discriminatedMapId = discriminator.getMapIdFor(String.valueOf(value));
       if (configuration.hasResultMap(discriminatedMapId)) {
         resultMap = configuration.getResultMap(discriminatedMapId);
         Discriminator lastDiscriminator = discriminator;
         discriminator = resultMap.getDiscriminator();
         if (discriminator == lastDiscriminator || !pastDiscriminators.add(discriminatedMapId)) {
           break;
         }
       } else {
         break;
       }
     }
     return resultMap;
   }
 
   private Object getDiscriminatorValue(ResultSet rs, Discriminator discriminator, String columnPrefix) throws SQLException {
     final ResultMapping resultMapping = discriminator.getResultMapping();
     final TypeHandler<?> typeHandler = resultMapping.getTypeHandler();
     return typeHandler.getResult(rs, prependPrefix(resultMapping.getColumn(), columnPrefix));
   }
 
   private String prependPrefix(String columnName, String prefix) {
     if (columnName == null || columnName.length() == 0 || prefix == null || prefix.length() == 0) {
       return columnName;
     }
     return prefix + columnName;
   }
 
   //
   // HANDLE NESTED RESULT MAPS
   //
 
   private void handleRowValuesForNestedResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
     final DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
     ResultSet resultSet = rsw.getResultSet();
     skipRows(resultSet, rowBounds);
     Object rowValue = previousRowValue;
     while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
       final ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
       final CacheKey rowKey = createRowKey(discriminatedResultMap, rsw, null);
       Object partialObject = nestedResultObjects.get(rowKey);
       // issue #577 && #542
       if (mappedStatement.isResultOrdered()) {
         if (partialObject == null && rowValue != null) {
           nestedResultObjects.clear();
           storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
         }
         rowValue = getRowValue(rsw, discriminatedResultMap, rowKey, null, partialObject);
       } else {
         rowValue = getRowValue(rsw, discriminatedResultMap, rowKey, null, partialObject);
         if (partialObject == null) {
           storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
         }
       }
     }
     if (rowValue != null && mappedStatement.isResultOrdered() && shouldProcessMoreRows(resultContext, rowBounds)) {
       storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
       previousRowValue = null;
     } else if (rowValue != null) {
       previousRowValue = rowValue;
     }
   }
 
   //
   // GET VALUE FROM ROW FOR NESTED RESULT MAP
   //
 
   private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, CacheKey combinedKey, String columnPrefix, Object partialObject) throws SQLException {
     final String resultMapId = resultMap.getId();
     Object rowValue = partialObject;
     if (rowValue != null) {
       final MetaObject metaObject = configuration.newMetaObject(rowValue);
       putAncestor(rowValue, resultMapId);
       applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, false);
       ancestorObjects.remove(resultMapId);
     } else {
       final ResultLoaderMapltLoaderMap.html#ResultLoaderMap">ResultLoaderMap lazyLoader = new ResultLoaderMap();
       rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
       if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
         final MetaObject metaObject = configuration.newMetaObject(rowValue);
         boolean foundValues = this.useConstructorMappings;
         if (shouldApplyAutomaticMappings(resultMap, true)) {
           foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
         }
         foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
         putAncestor(rowValue, resultMapId);
         foundValues = applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, true) || foundValues;
         ancestorObjects.remove(resultMapId);
         foundValues = lazyLoader.size() > 0 || foundValues;
         rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
       }
       if (combinedKey != CacheKey.NULL_CACHE_KEY) {
         nestedResultObjects.put(combinedKey, rowValue);
       }
     }
     return rowValue;
   }
 
   private void putAncestor(Object resultObject, String resultMapId) {
     ancestorObjects.put(resultMapId, resultObject);
   }
 
   //
   // NESTED RESULT MAP (JOIN MAPPING)
   //
 
   private boolean applyNestedResultMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String parentPrefix, CacheKey parentRowKey, boolean newObject) {
     boolean foundValues = false;
     for (ResultMapping resultMapping : resultMap.getPropertyResultMappings()) {
       final String nestedResultMapId = resultMapping.getNestedResultMapId();
       if (nestedResultMapId != null && resultMapping.getResultSet() == null) {
         try {
           final String columnPrefix = getColumnPrefix(parentPrefix, resultMapping);
           final ResultMap nestedResultMap = getNestedResultMap(rsw.getResultSet(), nestedResultMapId, columnPrefix);
           if (resultMapping.getColumnPrefix() == null) {
             // try to fill circular reference only when columnPrefix
             // is not specified for the nested result map (issue #215)
             Object ancestorObject = ancestorObjects.get(nestedResultMapId);
             if (ancestorObject != null) {
               if (newObject) {
                 linkObjects(metaObject, resultMapping, ancestorObject); // issue #385
               }
               continue;
             }
           }
           final CacheKey rowKey = createRowKey(nestedResultMap, rsw, columnPrefix);
           final CacheKey combinedKey = combineKeys(rowKey, parentRowKey);
           Object rowValue = nestedResultObjects.get(combinedKey);
           boolean knownValue = rowValue != null;
           instantiateCollectionPropertyIfAppropriate(resultMapping, metaObject); // mandatory
           if (anyNotNullColumnHasValue(resultMapping, columnPrefix, rsw)) {
             rowValue = getRowValue(rsw, nestedResultMap, combinedKey, columnPrefix, rowValue);
             if (rowValue != null && !knownValue) {
               linkObjects(metaObject, resultMapping, rowValue);
               foundValues = true;
             }
           }
         } catch (SQLException e) {
           throw new ExecutorException("Error getting nested result map values for '" + resultMapping.getProperty() + "'.  Cause: " + e, e);
         }
       }
     }
     return foundValues;
   }
 
   private String getColumnPrefix(String parentPrefix, ResultMapping resultMapping) {
     final StringBuilder columnPrefixBuilder = new StringBuilder();
     if (parentPrefix != null) {
       columnPrefixBuilder.append(parentPrefix);
     }
     if (resultMapping.getColumnPrefix() != null) {
       columnPrefixBuilder.append(resultMapping.getColumnPrefix());
     }
     return columnPrefixBuilder.length() == 0 ? null : columnPrefixBuilder.toString().toUpperCase(Locale.ENGLISH);
   }
 
   private boolean anyNotNullColumnHasValue(ResultMapping resultMapping, String columnPrefix, ResultSetWrapper rsw) throws SQLException {
     Set<String> notNullColumns = resultMapping.getNotNullColumns();
     if (notNullColumns != null && !notNullColumns.isEmpty()) {
       ResultSet rs = rsw.getResultSet();
       for (String column : notNullColumns) {
         rs.getObject(prependPrefix(column, columnPrefix));
         if (!rs.wasNull()) {
           return true;
         }
       }
       return false;
     } else if (columnPrefix != null) {
       for (String columnName : rsw.getColumnNames()) {
         if (columnName.toUpperCase().startsWith(columnPrefix.toUpperCase())) {
           return true;
         }
       }
       return false;
     }
     return true;
   }
 
   private ResultMap getNestedResultMap(ResultSet rs, String nestedResultMapId, String columnPrefix) throws SQLException {
     ResultMap nestedResultMap = configuration.getResultMap(nestedResultMapId);
     return resolveDiscriminatedResultMap(rs, nestedResultMap, columnPrefix);
   }
 
   //
   // UNIQUE RESULT KEY
   //
 
   private CacheKey createRowKey(ResultMap resultMap, ResultSetWrapper rsw, String columnPrefix) throws SQLException {
     final CacheKeyKey.html#CacheKey">CacheKey cacheKey = new CacheKey();
     cacheKey.update(resultMap.getId());
     List<ResultMapping> resultMappings = getResultMappingsForRowKey(resultMap);
     if (resultMappings.isEmpty()) {
       if (Map.class.isAssignableFrom(resultMap.getType())) {
         createRowKeyForMap(rsw, cacheKey);
       } else {
         createRowKeyForUnmappedProperties(resultMap, rsw, cacheKey, columnPrefix);
       }
     } else {
       createRowKeyForMappedProperties(resultMap, rsw, cacheKey, resultMappings, columnPrefix);
     }
     if (cacheKey.getUpdateCount() < 2) {
       return CacheKey.NULL_CACHE_KEY;
     }
     return cacheKey;
   }
 
   private CacheKey../../../../../org/apache/ibatis/cache/CacheKey.html#CacheKey">CacheKey./../../../org/apache/ibatis/cache/CacheKey.html#CacheKey">CacheKey combineKeys(CacheKey../../../../../org/apache/ibatis/cache/CacheKey.html#CacheKey">CacheKey rowKey, CacheKey parentRowKey) {
     if (rowKey.getUpdateCount() > 1 && parentRowKey.getUpdateCount() > 1) {
       CacheKey combinedKey;
       try {
         combinedKey = rowKey.clone();
       } catch (CloneNotSupportedException e) {
         throw new ExecutorException("Error cloning cache key.  Cause: " + e, e);
       }
       combinedKey.update(parentRowKey);
       return combinedKey;
     }
     return CacheKey.NULL_CACHE_KEY;
   }
 
   private List<ResultMapping> getResultMappingsForRowKey(ResultMap resultMap) {
     List<ResultMapping> resultMappings = resultMap.getIdResultMappings();
     if (resultMappings.isEmpty()) {
       resultMappings = resultMap.getPropertyResultMappings();
     }
     return resultMappings;
   }
 
   private void createRowKeyForMappedProperties(ResultMap resultMap, ResultSetWrapper rsw, CacheKey cacheKey, List<ResultMapping> resultMappings, String columnPrefix) throws SQLException {
     for (ResultMapping resultMapping : resultMappings) {
       if (resultMapping.getNestedResultMapId() != null && resultMapping.getResultSet() == null) {
         // Issue #392
         final ResultMap nestedResultMap = configuration.getResultMap(resultMapping.getNestedResultMapId());
         createRowKeyForMappedProperties(nestedResultMap, rsw, cacheKey, nestedResultMap.getConstructorResultMappings(),
             prependPrefix(resultMapping.getColumnPrefix(), columnPrefix));
       } else if (resultMapping.getNestedQueryId() == null) {
         final String column = prependPrefix(resultMapping.getColumn(), columnPrefix);
         final TypeHandler<?> th = resultMapping.getTypeHandler();
         List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
         // Issue #114
         if (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH))) {
           final Object value = th.getResult(rsw.getResultSet(), column);
           if (value != null || configuration.isReturnInstanceForEmptyRow()) {
             cacheKey.update(column);
             cacheKey.update(value);
           }
         }
       }
     }
   }
 
   private void createRowKeyForUnmappedProperties(ResultMap resultMap, ResultSetWrapper rsw, CacheKey cacheKey, String columnPrefix) throws SQLException {
     final MetaClass metaType = MetaClass.forClass(resultMap.getType(), reflectorFactory);
     List<String> unmappedColumnNames = rsw.getUnmappedColumnNames(resultMap, columnPrefix);
     for (String column : unmappedColumnNames) {
       String property = column;
       if (columnPrefix != null && !columnPrefix.isEmpty()) {
         // When columnPrefix is specified, ignore columns without the prefix.
         if (column.toUpperCase(Locale.ENGLISH).startsWith(columnPrefix)) {
           property = column.substring(columnPrefix.length());
         } else {
           continue;
         }
       }
       if (metaType.findProperty(property, configuration.isMapUnderscoreToCamelCase()) != null) {
         String value = rsw.getResultSet().getString(column);
         if (value != null) {
           cacheKey.update(column);
           cacheKey.update(value);
         }
       }
     }
   }
 
   private void createRowKeyForMap(ResultSetWrapper rsw, CacheKey cacheKey) throws SQLException {
     List<String> columnNames = rsw.getColumnNames();
     for (String columnName : columnNames) {
       final String value = rsw.getResultSet().getString(columnName);
       if (value != null) {
         cacheKey.update(columnName);
         cacheKey.update(value);
       }
     }
   }
 
   private void linkObjects(MetaObject metaObject, ResultMapping resultMapping, Object rowValue) {
     final Object collectionProperty = instantiateCollectionPropertyIfAppropriate(resultMapping, metaObject);
     if (collectionProperty != null) {
       final MetaObject targetMetaObject = configuration.newMetaObject(collectionProperty);
       targetMetaObject.add(rowValue);
     } else {
       metaObject.setValue(resultMapping.getProperty(), rowValue);
     }
   }
 
   private Object instantiateCollectionPropertyIfAppropriate(ResultMapping resultMapping, MetaObject metaObject) {
     final String propertyName = resultMapping.getProperty();
     Object propertyValue = metaObject.getValue(propertyName);
     if (propertyValue == null) {
       Class<?> type = resultMapping.getJavaType();
       if (type == null) {
         type = metaObject.getSetterType(propertyName);
       }
       try {
         if (objectFactory.isCollection(type)) {
           propertyValue = objectFactory.create(type);
           metaObject.setValue(propertyName, propertyValue);
           return propertyValue;
         }
       } catch (Exception e) {
         throw new ExecutorException("Error instantiating collection property for result '" + resultMapping.getProperty() + "'.  Cause: " + e, e);
       }
     } else if (objectFactory.isCollection(propertyValue.getClass())) {
       return propertyValue;
     }
     return null;
   }
 
   private boolean hasTypeHandlerForResultObject(ResultSetWrapper rsw, Class<?> resultType) {
     if (rsw.getColumnNames().size() == 1) {
       return typeHandlerRegistry.hasTypeHandler(resultType, rsw.getJdbcType(rsw.getColumnNames().get(0)));
     }
     return typeHandlerRegistry.hasTypeHandler(resultType);
   }
 
 }